Jan Joosten takes up the question of the nature of the BH verbal system, arguing that the qatal/yiqtol forms do not primarily express the aspectual opposition between perfect/imperfect. Instead, he argues that, while the qatal does primarily express perfect aspect, the main role of the yiqtol is future/modal.
His first argument is that the yiqtol form is not regularly used to express the real present or an attendant circumstance in the past, the two most prominent functions of the imperfect in aspect languages. The primary cases where yiqtol appears to be used as a real present are in questions, but questions are inherently “modal”. In declarative sentences the predicative participle is the usual form for real present. The participle can also be used with the presentative particles הנה and הלא, highlighting its use as a real present.
In Joosten’s example, “John was reading when I entered the room,” the form “was reading” is imperfective and describes the attendant circumstance for the perfect form “entered”. Again, in BH the regular form for attendant circumstance is not the yiqtol, but the participle as shown in 2 Sam 18:24:
וְדָוִ֥ד יוֹשֵׁ֖ב בֵּין־שְׁנֵ֣י הַשְּׁעָרִ֑ים וַיֵּ֨לֶךְ הַצֹּפֶ֜ה אֶל־גַּ֤ג הַשַּׁ֙עַר֙
David was sitting between the two gates when the watchman went to the roof of the gate…
The yiqtol form is indeed used for iterative/durative action in the past, which is a function of the imperfect in aspect languages. However, Joosten argues that repetitive action has no inherent relationship to the notion of imperfect aspect and may only be associated with imperfect verbal forms accidentaly. In fact, many aspect languages use perfective forms for repetitive action and others use modal forms. Again, the iterative use of yiqtol may reflect its modal function rather than imperfective.
Therefore, Joosten concludes that the primary role of yiqtol is for “action which has not yet begun”, whether it is simple future or modal. If so, yiqtol should not be understood in opposition to the perfect qatal, but in comparison with the other modal forms such as weqatal, cohortative, jussive, and imperative.